1. Field of the Invention
This application relates to a control method and a device thereof for controlling a filled water volume when a filling water test (such as a pressure withstanding test, a leak test and the like) is needed for a fluid space (a storage fluid space).
A filling water test for proving pressure withstanding performance is often required for a vessel that forms a fluid space such as a liquid storage tank or a gas storage tank, by inducing and keeping water inside the fluid space, when the erection of the vessel is completed.
In conventional practices as to the filling water test, clean water such as industrial water or fresh water is used; however, in a case when the filling water test is performed at a place where clean water is hard-to-get, for instance, at many sites in South and Central America, Africa, and the Near and Middle East, a vast amount of clean water has to be purchased; as a result, the expenditure of money for the test becomes enormous. Thus, the filling water test is performed by use of salt containing water (such as seawater) that can be relatively inexpensive to purchase, in a case where the inner surface of the vessel (such as tanks) is resistant to the corrosion caused by the salt containing water.
2. Background of the Invention
However, the vessel that forms the fluid space (a storage fluid space) is often provided with at least one piping system inside the space, thereby the piping system is not necessarily resistant to corrosion even though the inner surface of the vessel (such as tanks) is resistant to corrosion. In these cases, corrosion prevention is required for the piping system when a filling water test by use of salt containing water is performed; whereby, the piping system is not arranged in the filling water space during the filling water test (namely, if the piping system is once installed in the fluid space prior to the filling water test, then the piping system is removed outside), or a corrosion prevention treatment for the piping system is performed.
A concrete example in which the piping system in the fluid space is removed during the filling water test is a case where the vessel forming the fluid space (a storage fluid space) is a LNG tank storing liquefied natural gas (LNG); thereby, the piping system inside the space is used for charging LNG inside the space and discharging LNG outside the space. In general, the inner surface of the LNG tank is that of stainless steel (such as Cr-9Ni stainless steel) that has excellent strength and toughness in a low temperature use-environment (in a cryogenic environment), while the piping inside the fluid space is made of stainless steel that may corrode in a salt containing water environment in a case of the filling water test. In the cases like this, as shown in FIG. 5 that explains the steps as to a conventional filling water test, the test is performed under the condition that the piping system inside the fluid space is not arranged during the test; after the filling water test is finished, the piping system is installed in the fluid space.
In consultation with FIG. 5, the steps of the conventional filling water test in which salt containing water, namely, seawater is used will now be explained. When the erection of a LNG tank 1 is completed, a temporary piping system 50 is arranged between the LNG tank 1 and a sea 51. In addition, there are provided a pump 52 that charges seawater into the LNG tank 1 through the temporary piping system 50 and a pump 53 that discharges the charged seawater through the temporary piping system 50. After the arrangement regarding the temporary piping system 50 and the pumps 52 and 53 is finished, seawater is charged into the LNG tank 1 by use of the pump 52. When the LNG tank 1 is fully filled with seawater after the seawater charging, the filled state is kept for a fixed time period; then, the seawater inside the LNG tank is discharged back to the sea 51. On an as needed basis, a buffer pool 54 is sometimes provided on a part way of the temporary piping system. After the seawater discharge is finished, the temporary piping system 50 is removed, and an inside piping system 5 that the storage fluid space is provided with is installed.
According to the conventional method of the filling water test as depicted in FIG. 5, the inside piping system that is provided inside the tank can be free from corrosion, since the inside piping system is placed outside of the tank during the filling water test; however, since the installation of the inside piping system is performed after the filling water test is finished, the tank erection time is prolonged due to the time required for the filling water test; thus, the erection cost including the inspection cost increases.
On the other hand, regarding a corrosion protection method for the inner surfaces of the tank in a case of the filling water test, the patent reference 1 discloses a method in which a plurality of welding parts as to the inside surface of the tank are vinyl-covered by uses of double-face tape; further, the patent reference 2 discloses a method in which Zn (zinc) coating material is applied to a plurality of welding parts as to the inside surface of the tank.
According to the disclosures of the references 1 and 2, however, it requires a plenty of time to apply the corrosion protection treatments to the potentially corrosive parts of the piping system installed inside the tank, in a case where the surface area of the pipes in the piping system is large: thus, the corrosion protection treatments according to the disclosures also require a plenty of time, prolonging the erection schedule as is the case in the manner where the inside piping system is not installed during the filling water test that FIG. 5 explains concretely.